Re: force prop question
Without knowing your current RPM at wide open throttle and without knowing your top speed, it is difficult to tell.
Knowing that engine though, I would say that a 15 pitch on a 19 foot boat is too little unless you are carrying a heavy load. 17 pitch should be more like it, but of course, remember that I am dealing without starting numbers.
You want that engine to run in the 4500-5500 RPM range and the higher end is better.
Generally, a cup in the prop will reduce your WOT RPM by about 2-400 RPM. In the same pitch, it will not give more speed but will give better holding and less cavitation in sharp turns. Sometimes, you can run a cupped prop trimmed higher. Because of that, you do get a little more bow lift and a little more speed.---MAYBE!
I have a mental problem with the black flared "semi-cleaver" aluminum prop. I just don't like them. To me, they seem to bog down the engine. I prefer the older Force props or even Chrysler props. Third choice is the Michigan stainless cupped props. In my mind these seem to perform better. Stainless usually gives 200-400 RPM more than the equivalent aluminum prop. Usually I use either a 17 pitch cupped or a 19 pitch uncupped.
I recently rebuilt a 125 for a guy. He had it on a 18 foot bass boat and with the prop he had on--either 13 X 15 or 17 pitch, he did 40 top speed at 6000 RPM. I switched him to a Chrysler 13 X 19 stainless uncupped and his speed went up to 47 at around 5500 RPM
BUT: You need a tach and speedometer or GPS to play with props.
See my private message to you. Hmmmm! can't seem to send you a PM. If you are intersted in a stainless prop PM me.
BTW: The avatar in the upper port corner is my son piloting a 15 foot Glastron with a 1976 Chrysler 90 just south of Turkey point.
